As is known, operating electronic devices produce heat. This heat should be removed from the devices in order to maintain device junction temperatures within desirable limits. Failure to remove the heat thus produced results in increased device temperatures, potentially leading to thermal runaway conditions. Several trends in the electronics industry have combined to increase the importance of thermal management, including heat removal for electronics devices, including technologies where thermal management has traditionally been less of a concern, such as CMOS. In particular, the need for faster and more densely packed circuits has had a direct impact on the importance of thermal management. First, power dissipation, and therefore heat production, increases as device operating frequencies increase. Second, increased operating frequencies may be possible at lower device junction temperatures. Further, as more and more devices are packed onto a single chip, power density (Watts/cm2) increases, resulting in the need to remove more power from a given size chip or module. Additionally, a common packaging configuration for many large computer systems today is a multi-drawer rack, with each drawer containing one or more processor modules along with associated electronics, such as memory, power and hard drive devices. These drawers are removable units so that in the event of failure of an individual drawer, the drawer may be removed and replaced in the field. A problem with this configuration is the increase in heat flux at the electronics drawer level. The above-noted trends have combined to create applications where it is no longer desirable to remove heat from modern devices solely by traditional air cooling methods, such as by using traditional air cooled heat sinks. These trends are likely to continue, furthering the need for alternatives to traditional air cooling methods.
One approach to avoiding the limitations of traditional air cooling is to use a cooling liquid. As is known, different liquids provide different cooling capabilities. In particular, liquids such as refrigerants or other dielectric fluids (e.g., fluorocarbon fluid) exhibit relatively poor thermal conductivity and specific heat properties, i.e., when compared to liquids such as water or other aqueous fluids. Dielectric liquids have an advantage, however, in that they may be placed in direct physical contact with electronic devices and interconnects without adverse affects such as corrosion or electrical short circuits. For example, U.S. Pat. No. 6,052,284, entitled “Printed Circuit Board with Electronic Devices Mounted Thereon”, describes an apparatus in which a dielectric liquid flows over and around several operating electronic devices, thereby removing heat from the devices. Similar approaches are disclosed in U.S. Pat. No. 5,655,290, entitled “Method for Making a Three-Dimensional Multichip Module” and U.S. Pat. No. 4,888,663, entitled “Cooling System for Electronic Assembly”.
Other cooling liquids, such as water or other aqueous fluids, exhibit superior thermal conductivity and specific heat compared to dielectric liquids. Water-based coolants, however, must be kept from physical contact with electronic devices and interconnects, since corrosion and electrical short circuit problems are likely to result from such contact. Various methods have been disclosed for using water-based coolants, while providing physical separation between the coolant and the electronic devices. For example, U.S. Pat. No. 4,531,146, entitled “Apparatus for Cooling High-Density Integrated Circuit Packages”, discloses the use of a conductive foil barrier; U.S. Pat. No. 4,879,629, entitled “Liquid Cooled Multi-chip Integrated Circuit Module Incorporating A Seamless Compliant Member for Leakproof Operation”, and IBM Technical Disclosure Bulletin Vol. 20, No. 2, July 1977, entitled “Liquid Cooled Module with Compliant Membrane”, disclose the use of a flexible barrier with thermal conduction enhancements (thermal studs and heatsinks, respectively); and U.S. Pat. No. 4,381,032, entitled “Apparatus for Cooling High-Density Integrated Circuit Packages”, and U.S. Pat. No. 5,294,830, entitled “Apparatus for Indirect Impingement Cooling of Integrated Circuit Chips”, disclose the use of flexible barriers, where pistons are used to maintain contact between the barrier and the devices to be cooled. The above-incorporated, co-pending patent application entitled “Electronic Device Substrate Assembly With Mulilayer Impermeable Barrier and Method of Making”, describes an electronic device substrate assembly with a multilayer impermeable barrier which provides high effective thermal conductivity between a device to be cooled and a water-based coolant, while simultaneously maintaining physical separation between the coolant and electronic devices and minimizing mechanical stresses caused by mismatches in the thermal coefficients of expansion of various materials within the device assembly.
Notwithstanding the above, there remains a large and significant need to provide further useful cooling apparatus enhancements for facilitating cooling of electronic circuit devices such as electronic modules disposed, e.g., in a multi-drawer electronics rack.